Publications

With conventional marine streamer surface seismic data, a data "gap" exists in the low frequency range from zero to approximately 6-12 Hertz. This is due to the free surface "ghost" effect of towing sources and streamers beneath the sea surface. As a consequence, typical conventional data cannot yield a bandwidth beyond approximately 2.7 octaves irrespective of tow depth. For inversion, low frequencies, not described by the seismic, are generally modeled using interpolated well data. However, the absence of low frequencies, places greater dependency on the well data and hence greater uncertainly and bias into the inversion. Typically this well information is either very sparse spatially or, completely unavailable, thereby providing a challenge.This paper will describe an acquisition, processing and inversion method that can fill the frequency "gap" in the data spectrum without the need for well data. By use of multi level sources and streamers the gap can be minimized in this crucial low frequency zone. A conventional "shallow" cable 3D geometry is augmented by a sparse set of deeper cables. This process is known as DISCover.Data from a 3D case study was acquired using DISCover over the NW Shelf offshore Australia. The streamer spread consisted of six shallow streamers towed at a depth of 6 m and two deeper streamers towed at a depth of 20 m. Results showed considerable low frequency improvement of around 12dB in signal-to-noise ratio below 10Hz. With this technique the bandwidth of the data was extended from 2.7 octaves for the 6m cables alone, to 4 octaves for the combined data. The consequent improvement to the inversion will also be shown.